A seat apparatus for a vehicle disclosed in JP2750943 is well known. When the vehicle lateral accelerations are continuously detected, the seat apparatus determines that the vehicle is driven on a road having plural curves, such as a winding road, and then a supporting operation is executed. During the supporting operation, the seat apparatus is controlled in order to retain a side support portion to a position where a human body is supported thereby (hereinbelow, referred also to as a supporting position). According to the seat apparatus disclosed in JP2750943, the side support portion is retained to the supporting position without depending on an electronic map data. As a result, an occupant of the vehicle seat may not feel frequent actuations of the supporting operation.
However, because the seat apparatus disclosed in JP2705943 determines that the vehicle is driven on the winding road when the lateral acceleration is continuously generated at the vehicle, when the vehicle is driven on a winding road that has, for example, two curves including a straight portion therebetween, the seat apparatus may continuously retain the side support portion to the supporting position. As a result, even when the vehicle is driven on the straight portion between the curves where the occupant basically needs to be supported less firmly than on the curve, the occupant may still feel firmly pressured by the side support portion.
On the other hand, a vehicle controlling apparatus disclosed in JP2005088834A includes a suspension control device and a navigation device. The navigation device determines that the vehicle is driven on a winding road that has, for example, two curves (e.g., a first curve and a second curve) including a straight portion therebetween, based on electronic map data, and the suspension control device controls a suspension on the basis of the determination of the navigation device. In this configuration, even when the navigation device determines that the vehicle is driven on the straight portion, the suspension is controlled so as to be at a maximum controlling level of the first curve. In other words, according to the vehicle controlling device disclosed in JP2005088834A, when the straight portion exists between the two curves, because the navigation device determines that the vehicle is driven on the winding road based on the electronic map data, the suspension is continuously controlled during the entire winding road. In the light of this configuration, it is conceivable that a side support portion may be controlled in the same manner as the suspension is controlled by the vehicle controlling apparatus.
However, if the side support portion is controlled in the same manner as the suspension is controlled by the vehicle controlling apparatus, when the vehicle is driven on the straight portion of the winding road, because the side support portion is controlled so as to be at a maximum control level of the first curve, the occupant needs to be supported less firmly than when the vehicle is driven on the curve and thus may continuous pressure.
A need thus exists for a seat apparatus for a vehicle which is not susceptible to the drawback mentioned above.